JPS62172683A - Manufacture of self-control heating unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a self-regulating heating element, which comprises as a heat source at least one resistor made of a material having a positive temperature coefficient of electrical resistance (hereinafter referred to as a PTC resistor).

U.S. Pat. No. 4,147,927 discloses that one or more resistors are disposed between metal bodies, and the metal body exchanges heat with the inner surface of the casing on the side not facing the one or more resistors. A heating element as described above is described which is characterized in that the heating element contacts in an adjacent manner.

According to the above-mentioned patent specification, the casing can be made of glass, ceramics or thermally conductive elastic synthetic resin, if desired with a metallic outer casing.

U.S. Pat. No. 4,104,509 discloses that the heating element is made of a vulcanized synthetic resin material that can withstand the maximum operating temperature of the heating element, an electrically insulating, thermally conductive metal compound, and, if necessary, a filler material, as required in practice. The casing material that best satisfies the requirements is described.

The vulcanized synthetic resin material is preferably silicone rubber. Magnesium oxide, trivalent iron oxide or aluminum oxide can be used as the thermally conductive metal compound and silicon dioxide as the filler material.

Since the assembly is connected to the main line, it is desirable for safety to surround the PTC resistor and the metal body surrounding it with double insulation. For example, errors in casing composition or hardening depth can cause the heating element casing to crack during use;
It is then very important that there is a second casing of a more elastic material, which protects the user of the heating element from coming into contact with live metal parts.

Molding the interfitable parts of the casing or encapsulating the molded part with a second material is a process which has too many disadvantages in practice and cannot be automated.

Another possibility is to encapsulate the assembly of PTC resistor and surrounding metal part with an insulating synthetic resin foil, for example a polyimide foil, before sliding it into the molded casing. However, this method is also complex and expensive.

The method according to the invention is characterized in that an elastomer layer is provided from solution on the inner, outer or both inner and outer surfaces of the molded casing.

The solution provides the elastomer in the form of layers.

The viscosity of the elastomer is higher than that of the molded part by 200 to 10
Preferably, it has a viscosity in the range of 00000 mPa, sec. This means that the layer has a higher elasticity than the molded part.

The elastomer may be an addition or condensation form of a two-component silicone resin.

The two-component silicone resin may be composed of a polysiloxane polymer grafted with reactive vinyl groups and a hydrosiloxane, and may further contain a platinum salt as a catalyst. When applying a layer, a solution of a single solvent, such as xylene, or a mixture of solvents is used, which is applied and then evaporated. Filler materials such as metal oxides, dyes or stabilizers with high thermal conductivity can be added to the elastomer solution.

If the layer is to be applied to the outside of the molding, this can be done by dipping. The inner layer fills the molded part with a solution,
This is then poured out to form a layer of wall soil. It is preferred to vibrate the solution during contact with the pressed part so as to obtain a layer with a constant thickness.

After applying the solution, it is dried at, for example, 175°C for 10 minutes, and further dried at, for example, 200°C for 4 minutes to promote polymerization.
Heat for an hour.

The method according to the invention has many advantages.

Transferring the formed casing to a filling or dipping device can be easily automated. Furthermore, the diameter of the heating element is 3mm.
This thickness is preferred in practice. Furthermore, if a crack accidentally occurs in the molded part, the second casing provided by the liquid, which is more elastic, remains intact and locally separates from the molded part at the location of the crack. No exposed metal parts are exposed.

Next, the invention will be explained in more detail with reference to the accompanying drawings.

1 and 2 show resistors 1 and 2 with a positive temperature characteristic of resistance. These low antibodies are fixed between two semi-cylindrical metal bodies 3 and 4 made of aluminum, for example. For example, the inside of the casing 6 molded from vulcanized silicone rubber filled with magnesium oxide and silicon dioxide, and the space between the molded casing 6 and the metal bodies 3 and 4, is made of a silicone elastomer having a viscosity of 1Q6 mPa, sec at room temperature. Cover with layer 5.

FIG. 3 shows a heating element which differs from that of FIG. 1 only in that the layer 5 on the inside of the molding is replaced by a similar layer 9 on the outside of the molding.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of a heating element manufactured according to the present invention, Fig. 2 is a sectional view taken along the line ■-■ of the heating element of Fig. 1, and Fig. 3 is a longitudinal sectional view of a heating element manufactured according to the invention. It is a longitudinal cross-sectional view of another example. 1.2...Resistor 3.4...Semi-cylindrical metal body 5...Layer 6...Casing 9.
··layer

Claims (1)

[Claims] 1. At least one resistor made of a material having a positive temperature coefficient of electrical resistance is provided as a heat source, one or more resistors are disposed between metal parts, and the metal part In manufacturing a self-regulating heating element in which the heating element contacts the inner surface of a vulcanized or unvulcanized thermoplastic casing in a heat exchange manner on the side facing away from the resistor or resistors, the inner, outer or outer surfaces of the molded casing A method for producing a self-regulating heating element, characterized in that an elastomer layer is provided from solution on both sides. 2. The method according to claim 1, wherein the elastomer of the layer has a higher viscosity and elasticity than the material of the molded part. 3. The layer is formed by filling the molding section with an elastomer solution, then emptying the section, removing the solvent, and heating the elastomer to accelerate polymerization of the elastomer, as set forth in claim 1 or 2. Method. 4. Seal the layer by immersing the molded part in the elastomer solution, then removing the part, allowing excess solution to run off, and then heating the part to remove the solvent and promote polymerization of the elastomer. Claim 1 provided
or the method described in paragraph 2.